Thread cutting device on a sewing machine

ABSTRACT

A thread cutting arrangement for sewing machines including an arrangement in which the tension of the thread is released in both directions of movement of an axially moveable drive mechanism such that the thread tensioning mechanism is opened when the needle thread is caught. The movement of the drive mechanism is transmitted via a one-way coupling so that the opening of the thread tensioning mechanism is limited to the duration of the after pawal of the needle thread.

FIELD OF THE INVENTION

The present invention pertains to a thread cutting device for sewingmachines with a thread catcher. The thread catcher being actuated by anaxially moveable drive mechanism to perform a first movement stepcatching the needle thread and the shuttle thread, and a second movementstep whose direction is opposite to the first movement step in which thethreads are pulled out and fed to a stationary cutting blade. A threadtensioning mechanism is provided for the needle thread and a releasingmember for opening the thread tensioning mechanism during the threadpull operation. The releasing member being actuated by a cam rigidlyattached to the drive mechanism.

BACKGROUND OF THE INVENTION

A thread cutting device, in which an axially displaceable drivemechanism catches the needle thread and the shuttle thread in one of itsdirections of movement and pulls them out and feeds them to the cuttingblade in its other direction of movement, has become known from arealized sewing machine design. To control the releasing mechanism forthe thread tension, a cam actuating the release mechanism is fastened onthe drive mechanism. Even though this measure ensures a very simpledrive of the tensioning mechanism, it causes opening of the threadtensioning mechanism during the movement of the drive mechanism in bothdirections of movement. This leads to difficulties in catching the loopunder critical thread conditions and also to unequal thread ends afterthe cutting process.

SUMMARY AND OBJECTS OF THE INVENTION

It is an object of the present invention to design the releasingmechanism for thread tensioning in a thread cutting device with a threadcatcher actuated by an auxiliary moveable drive mechanism which performsa first movement step catching the needle thread and the shuttle threadand a second movement step whose direction is opposite to the firstmovement step wherein the threads are pulled out and fed to a stationarycutting blade. A thread tensioning mechanism is provided for the needlethread and a releasing member for opening the thread tensioningmechanism during the thread pull operation. The releasing member beingactuated by a cam rigidly attached to the drive mechanism so that thethread tensioning mechanism is opened only during the afterpull of theneedle thread.

According to the invention, a thread cutting device is provided forsewing machines with a thread catcher. The thread cutting device beingactuated by an axially moveable drive mechanism. The thread catcherperforms a first movement step catching the needle thread and theshuttle thread and a second movement step whose direction is opposite tothat of the first movement step in which the threads are pulled out andfed to a stationary cutting blade. A thread tensioning mechanism isprovided for the needle thread and a releasing member is providedopening the thread tensioning mechanism during the thread pulloperation. The releasing member can be actuated by a cam rigidlyattached to the drive mechanism. A one way coupling is provided for thereleasing member which is in action during the second movement step ofthe drive mechanism, the one way coupling being provided between thedrive mechanism and a linkage connected to the releasing member.

With the control according to the present invention, the threadtensioning mechanism now remains closed during the penetration of thethread catcher into the needle thread loop, so that the stability of theloop is preserved when it is being caught by the thread catcher. Thethread tensioning mechanism is opened only at the beginning of theafterpull of the needle thread and closes only when no more thread ispulled.

An embodiment of simple design of the one-way coupling is providedaccording to the invention in which the one-way coupling has a leveryielding in one direction. The lever pivoting during the first movementstep of the drive mechanism and remaining rigid during the secondmovement step of the drive mechanism.

The measure according to the invention in which the cam is limited by acam section rising in a wedge shaped manner at one end and by a radiallydropping cam section at the other end leads to slip-free opening of thethread tensioning mechanism and to immediate closing of the threadtensioning mechanism after a sufficient amount of needle thread has beenpulled in.

The various features of novelty which characterize the invention arepointed out with particularity in the claims annexed to and forming apart of this disclosure. For a better understanding of the invention,its operating advantages and specific objects attained by its uses,reference is made to the accompanying drawings and descriptive matter inwhich a preferred embodiment of the invention is illustrated.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a partially cut-away sectional view showing a sewing machinewith a control of the thread cutting device and of the thread tensioningmechanism according to the invention;

FIG. 1a is a sectional view showing the thread tensioning mechanism indetail;

FIG. 2 is a top view of part of the drive of the thread cutting andtensioning device shown in FIG. 1; and

FIGS. 3 through 5 show various positions of the cam and of the one-waycoupling for controlling the thread tension according to the invention.

FIG. 6 is a schematic representation of the shuttle together with thecut-off device;

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 shows the base plate 1 of a sewing machine, under which thehorizontal shuttle drive shaft 2 is mounted. The shaft is driven by alower main shaft 4 via a step-up gear 3. The shuttle 5 is fastened atthe front end of the shuttle drive shaft 2. It cooperates with theneedle 6 that can be moved up and down and fastened in a needle bar 6awhich is only schematically indicated. A thread cutting device 7, whosedesign and mode of operation are described in U.S. Pat. No. 3,173,392,is arranged under the base plate 1. The thread cutting device 7 has athread catcher 8, which is arranged coaxially with the shuttle 5 andcooperates with a cutting blade 9 fastened on the lower side of the baseplate 1. The thread catcher 8 is fastened on a supporting arm 10 whichis connected to a ring 11 that loosely surrounds the shuttle drive shaft2. The ring is secured in the axial direction and is mounted freelyrotatably in loop 12 that is fastened under the base plate 1. Aconnecting rod 13 is hinged to the supporting arm 10, and the connectingrod 13 is connected to an arm of an angle lever 14 which is supported bya bearing block 15 that forms an integral part of the housing. The otherarm of the angle lever 14 is connected to a drive mechanism 17 for thethread catcher 8 via a bar 16.

To drive the thread catcher 8, a cam 18, which has a control groove 19as well as a control segment 20, is fastened on the main shaft 4. Adrive mechanism 21, designed as an axially displaceable shaft, ismounted in a support 22 fastened under the base plate 1 in parallel tothe main shaft 4 (cf. FIG. 2). A control lever 24, provided with aroller pin 23 as well as a releasing lever 25, is fastened on the drivemechanism 21. A pawl 28 equipped with a locking lug 26 and a stop 27 isloosely mounted on a sleeve 30 fastened in a side wall 29 of the support22 and is secured against axial displacement by the side wall 29 of thesupport 22 as well as by an end flange 30a of the sleeve 30. A spring 31wound around and is supported by the drive mechanism 21, which abuts thecontrol lever 24 at one end 3a and is supported by the pawl 28 at theother end 3b causes the pawl to swivel in the direction toward thecontrol segment 20 of the cam 18 and the roller pin 23 out of thecontrol groove 19. At the same time, the spring 31 acts as a compressionspring and displaces the drive mechanism 21 into its right-hand endposition, shown in FIG. 1, in which the roller pin 23 is opposite thecontrol groove 19 when the sewing machine is in the lowered needleposition.

An electromagnet 32, whose armature 33 is connected to an arm 35 of astarting lever 36 via an eye 34, is fastened in the support 22. Thestarting lever is mounted in the support 22 and is pivoted upward by atorsion spring 37 until a pivoted-down projection 38 comes into contactwith the locking lug 26 of the pawl 28 or--with the pawl in thepivoted-down position--until a stop 39 comes into contact with asetscrew 40 fastened adjustably in the support 22.

Before the threads are cut, they must be pulled out over a lengthsufficient for the subsequent stitch formation. This takes place withthe needle thread tensioning mechanism released. The thread tensioningmechanism 42 (FIG. 1a) for the needle thread consists of a sleeve 43with a longitudinally slotted setscrew 44 fastened in the machinehousing, wherein tensioning disks 45, 46 are arranged on the setscrewand the disks are compressed by a tension spring 48 adjustable by meansof a knurled nut 47 in order to exert a decelerating force on the needlethread. A releasing pin 49 is arranged in the sleeve 43 longitudinallydisplaceably, by means of which the tensioning disk 45 can be lifted offfrom the tensioning disk 46 against the action of the tension spring 4in order to open the thread tensioning mechanism 42.

A cam 50, whose surface is designed as a cam curve having a curvesection 51 rising in the shape of a wedge at one end and a straight andthen radially falling curve section 52 at the other end, is used toactuate the releasing pin 49, and consequently to release the threadtensioning mechanism 42. A one-way coupling 53, which is arranged on alever arm 54 mounted on the support 22, cooperates with the cam 50. Theone-way coupling 53 consists of a segment-shaped lever 55, which ismounted pivotably on lever arm 54 and cooperates with the cam 50, aswell as a stop 57, which is in contact with a pin 59 fastened in thelever arm 54 under the action of a torsion spring 58.

The lever arm 54 is rotated by a torsion spring 60 until a lateralcontact surface 54a or the one-way coupling 53 comes into contact withthe cam 50. The torque exerted by the torsion spring 60 considerablyexceeds the torque exerted by the torsion spring 58. The lever arm 54 isconnected to an angle lever 62 mounted on the machine housing via a bar61. A push rod 63, which carries at its front end a releasing member 65provided with an oblique surface 64 (FIG. 1a), is hinged to the anglelever.

Assuming that the sewing machine is running and the roller pin 23 is inits position outside the cam groove 19 of the cam 18 rotating togetherwith the main shaft 4, the thread catcher 8 with its drive member 21 isin its starting position, and the thread tensioning mechanism 42 for theneedle thread is closed, the device operates as follows: At the end ofthe seam, the sewing machine is briefly stopped by a needle positioningdevice in the lowered needle position, which is the starting positionfor thread cutting. The cam groove 19 in the cam 18 now assumes aposition in which the roller pin 23 on the control lever 24 can be movedinto the cam groove 19 by a single swiveling movement. The cam 50 andthe one-way coupling 53 are in the position shown in FIG. 3, in whichthe thread tensioning mechanism 42 is closed.

By actuating a switch while depressing the pedal of the sewing machinefor the reverse direction, the electromagnet 32 is briefly energized andthe drive motor of the sewing machine is turned on immediatelythereafter. The starting lever 36 is pulled down by the armature 33 ofthe electromagnet 32 and it pushes the roller pin 23 into the cam groove19 via the releasing lever 25 and the control lever 24. At the sametime, the spring 31 pivots the pawl 28, whose locking lug 26 liesagainst the projection 38 on the starting lever 36 and thus locks theposition of the roller pin 23 pushed into the cam groove 19.

During the subsequent revolution of the main shaft 4 in the direction ofarrow A, which is necessary for the thread cutting, the cam groove 19,extending in the axial direction, displaces the drive mechanism 21--viathe control lever 24--from its resting position to the left,corresponding to a first section of the cam groove 19. The drivemechanism 21 now moves the thread catcher 8 via the angle lever 14 andthe connecting rod 13 and into the widened needle thread loop caught bythe shuttle 5 and thus catches the leg of the needle thread loop leadingto the fabric to be sewn, as well as the shuttle thread, in the knownmanner.

During its displacement to the left, the cam section 52 hits the lever55 and rotates same against the force of the torsion spring 58, so thatthe lever arm 54 remains in its resting position determined by thecontact between the contact surface 54a and the cam section 52 duringthe displacement of the drive mechanism 21 to the left, and while thewedge-shaped curve section 51 passes by, the lever 55 again returns intoits resting position, in which it is in contact with the pin 59.

After the loop of the needle thread has fallen off from the shuttle 5,the drive mechanism 21 is moved to the right as a consequence of thecurved design of the cam groove 19 (FIG. 5). The wedge-shaped camsection 51 of the cam 50 now moves toward the lever 55 of the one-waycoupling 53 and thus pivots the lever arm 54, which releases the threadtensioning mechanism 42 for the needle thread via the bar 51, the anglelever 62 and the push rod 63 in such a way that the releasing pin 49 isaxially displaced by the oblique surface 64 of the releasing member 65,as a result of which the tensioning disk 45 is lifted off from thetensioning disk 46 against the force of the tension spring 48.

At the same time, the thread catcher 8 pulls thread from the shuttlethread reserve and the needle thread reserve due to the movement of thedrive mechanism 21 to the right until the cutting blade 9 fastened onthe lower side of the base plate 1 cuts off both threads shortly beforethe end of this movement.

Immediately thereafter, the cam section 52 of the cam 50 moves past thelever 55 of the one-way coupling 53, and the lever 55 can drop in behindthe cam section 52 under the pressure of the torsion spring 60, so thatthe lever arm 54 can come into contact with its lateral contact surface54a with the axially parallel surface of the cam section 52 of the cam50. This dropping off of the lever 55 from the cam section 52 bringsabout immediate closure of the thread tensioning mechanism 42 via thetensioning release linkage.

During the further residual rotation of the main shaft 4 until thesewing machine is turned off in the raised needle position, the segment20 pivots the pawl 28 over the stop 27, so that the locking lug 26 againreleases the starting lever 36. The starting lever is pivoted upward bythe torsion spring 37 until it comes into contact with the projection 38at pin 40. As a result, the spring 31 is able to push the control lever24 away from the cam 18, so that the roller pin 23 is lifted out of thecam groove 19. The sewing machine will then be stopped with the threadlever in the raised position and is ready for the next sewing operation.

While a specific embodiment of the invention has been shown anddescribed in detail to illustrate the application of the principles ofthe invention, it will be understood that the invention may be embodiedotherwise without departing from such principles.

We claim:
 1. A thread cutting arrangement for sewing machines,comprising: an axially moveable drive mechanism; thread catcher means,actuated by said axially moveable drive mechanism, said thread catchermeans performing a first movement step catching a needle thread and ashuttle thread, and a second movement step, having a direction which isopposite to said first movement step, in which the needle thread and theshuttle thread are pulled out and fed to a stationary cutting blade; athread tensioning mechanism for tensioning the needle thread; releasingmember means for disengaging the thread tensioning mechanism to open thethread tensioning mechanism during the thread pull operation; a camarrangement rigidly attached to the drive mechanism for actuating thereleasing mechanism; a one-way coupling for the releasing member, actingduring the second movement step of the drive mechanism, said one-waycoupling being connected between the drive mechanism and a linkageconnected to the releasing member.
 2. A thread cutting device accordingto claim 1, wherein said one-way coupling arrangement includes a leveryielding in one direction, which pivots during the first movement stepof the drive mechanism and remains rigid during the second movement stepof the drive mechanism.
 3. A thread cutting arrangement according toclaim 1, wherein said cam is limited by a cam section rising inwedge-shaped manner at one end and by a radially dropping cam section atanother end.